EDITORIAL When cardiac resynchronization therapy may be harmful: time to wake up

This editorial refers to ‘Cardiac resynchronization therapy in patients with systolic heart failure and QRS interval <130 ms: insights from a meta-analysis ’ by R.M. Shah et al., on page 267–273. Cardiac resynchronization therapy (CRT) is one of the major break-throughs in heart failure (HF) management which has proven to reduce mortality and HF hospitalizations in patients with symptom-atic systolic HF and electrical dyssynchrony.1 –3 In later years, it has become apparent that the response to CRT is related to the magni-tude of QRS prolongation and the presence of left bundle branch block (LBBB).4,5 Importantly, it is also becoming increasingly clear that CRT may be harmful in patients with HF and narrow QRS. However, the clinical implications of these observations have not been extensively discussed or adopted. Shah et al.6 in a meta-analysis of four randomized controlled trials (RCTs) published in this issue of EP-Europace corroborate that CRT in patients with systolic HF and narrow QRS is associated with increased all-cause mortality. Since many patients in Europe have received CRT outside of the guideline recommendations7 including those with narrow QRS, the consequences of potential harm by CRT in such patients must be further discussed and acted upon. The most recent EuropeanHeratRhythmAssociation (EHRA)and European Society of Cardiology guidelines on cardiac pacing and CRT2 already state that CRT is not indicated in HF patients with narrow QRS (Class III, level of evidence B). Instead, CRT is indicated for HF patients with LBBB with QRS ≥150 ms (Class I, level of Evidence A) and for those with QRS 120–150 ms (Class I, level of Evidence B). For patients without LBBB, the class of recommenda-tions are lower. In these patients, CRT should be considered (Class IIa, level of Evidence B) if the QRS width is ≥150 ms and may be considered (Class IIb, level of Evidence B) in patients with the QRS duration of 120–150 ms. It is worthwhile reviewing the inclusion criteria in the RCTs on CRTover the last 15 years. In MUSTIC (MUltisite STimulation In Car